Getting a null pointer when testing a controller using MockMvc

I am getting a null pointer when unit testing a controller. The null pointer is occurring in the controller when calling a mocked service to get an id. I tried many things but I am still getting the same error.

Below is a snippet from the controller code where the null pointer is occurring:

@RestController
@RequestMapping(ELEMENTS_BASE_URI)
@EnableCommonRestHeaders
public class ElementController {
    @Autowired
    private ElementService elementService;
...
public ResponseEntity<ElementDto> createElement(
            @Valid @RequestBody ElementDto elementDto) {

        ElementDto saved = elementService.createElement(elementDto);

        HttpHeaders headers = new HttpHeaders();

        URI location = UriBuilder.builder(ELEMENT_LINK_URI)
                .pathVariable(ELEMENT_ID, saved.getId())
                .create();
        headers.setLocation(location);

        return new ResponseEntity<>(saved, headers, HttpStatus.CREATED);
    }
...

}

In the controller code above, The null pointer occurs at the line below: saved is null

   ElementDto saved = elementService.createElement(elementDto);

The test code is as below:

import static com.sas.fcs.networkbuild.util.matchers.JSONContentResultMatcher.jsonObject;
import static com.sas.fcs.networkbuild.util.matchers.JSONContentResultMatcher.jsonPath;

@RunWith(SpringJUnit4ClassRunner.class)
@WebMvcTest(controllers = ElementController.class, excludeAutoConfiguration = MockMvcSecurityAutoConfiguration.class)
@ActiveProfiles(value = {"test", "hsql", "disable-oauth2"})
@TestPropertySource("classpath:/test.properties")
public class ElementControllerTest {


    @MockBean
    private ElementService elementService;

    @Autowired
    ElementController elementController;

    @Autowired
    private MockMvc mockMvc;

    @Autowired
    private ObjectMapper mapper;

    @Before
    public void setUp() {
        mockMvc = MockMvcBuilders
                .standaloneSetup(elementController)
                .build();
    }

    @Test
    public void testCreateElementSuccess() throws Exception {
        ElementDto element = new ElementDto();
        element.setName("firstname");
        element.setModifiedTimeStamp(new Date());

        ElementDto createdElement = new ElementDto();
        String elementId = "123";
        createdElement.setId(elementId);
        createdElement.setName("firstname");
        createdElement.setLabel("firstname");
        createdElement.setAttribute(true);
        createdElement.setKeep(true);


        when(elementService.create(element)).thenReturn(createdElement);

        // make sure returns location with new element id
        mockMvc.perform(
                post(ServiceConstants.ELEMENTS_BASE_URI)
                     .content(mapper.writeValueAsBytes(element))
                     .accept(ElementDto.MEDIA_TYPE_JSON_VALUE)
                     .contentType(ElementDto.MEDIA_TYPE_JSON_VALUE))
                     .andExpect(status().isCreated())
                     .andExpect(header().string("Location",
                        Matchers.endsWith(ServiceConstants.SERVICE_URI + ServiceConstants.ELEMENTS_BASE_URI + "/" + elementId)))
                     .andExpect(header().string("Last-Modified", not(isEmptyString())))
                     .andExpect(jsonObject().is(createdElement))
                     .andExpect(jsonPath("name").value(element.getName()))
                     .andReturn();
    }
}

The line:

when(elementService.create(element)).thenReturn(createdElement);

does not seem to have any effect. Any help on this is really appreciated.

Regards, Firas